Optical networks comprise a plurality of optical network nodes which are connected to each other through optical fiber spans. Each optical fiber span can comprise at least one optical fiber through which an optical signal is transmitted from a transmitting network node to a receiving network node. The fibers used in an optical fiber span can comprise different optical fiber types. A wide variety of optical fiber types have been deployed in optical networks around the world over the past several decades. Different fiber manufacturers produce optical fibers with different characteristics. Further, each fiber manufacturer does develop different fiber designs over time. The resulting diversity of single-mode fiber types deployed over the recent years in optical networks led to the situation where many network operators of optical networks have only a limited access, knowledge or records about existing fibers, particularly if the fibers have been purchased or leased from third parties. The various deployed fiber types have quite a broad range of different fiber characteristics providing different transmission performance and impairments on optical signals propagating over the optical fibers. A fiber type of an optical fiber comprises key optical characteristics within a range of values which determine a specific range of performance of the optical network system, or require a specific parameter setting in the optical system. Because of the limited access, knowledge and/or records of existing or deployed optical fibers in an optical network there is a need to provide a method and apparatus for determination of the fiber types of optical fibers of an optical network.